Because the vaccine contains killed virus, the
influenza shot 
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cannot cause the flu. If you develop the flu after being
immunized, it may be because you were exposed to the flu virus before receiving
the injection or you were exposed to another virus that the vaccine did not
protect against.
Some minor side effects of the
immunization have been reported and may include:
- Discomfort at the site of the shot. This is the
most frequent side effect in adults and may last 1 to 2
days.
- Fever, vague feelings of weakness, and muscle aches. These
may occur 6 to 12 hours after the flu shot and last 1 to 2 days.
Acetaminophen or ibuprofen can help relieve any minor side
effects. Do not give aspirin to anyone younger than 20
because of the risk for developing
Reye syndrome.
No reports have been
confirmed of
Guillain-Barré syndrome developing in people as a
result of the influenza vaccine since the 1976 vaccination program. During that
year, the swine flu vaccine was associated with an increase in the syndrome.
Guillain-Barré syndrome is the only known possible fatal reaction to influenza
vaccine and is extremely rare. The risk of death from the flu vaccine is
estimated at 1 person out of 2 million and is significantly lower than the risk
of dying from complications caused by the flu.
